Rotating x-ray target

ABSTRACT

This invention relates to a rotating X-ray target made up of three metallic components, i.e., a molybdenum body, a focal track of an alloy of tungsten with one or more metal additives and a component present in the surface not exposed to electrons comprising tungsten alone or a tungsten alloy having a lesser amount of the additive metals.

United States Patent Machenschalk et al.

154] ROTATING X-RAY TARGET [72] Inventors: Rudolf Machenschalk; HerbertWagner, both of Reutte, Austria [73] Assignee: Schwarzkopf DevelopmentCorporation, New York, NY.

221 Filed: March 24, 1971 211 App1.No.: 127,507

[30] Foreign Application Priority Data March 25, 1970 Austria ..2792/70[52] US. Cl. ..313/330, 313/55, 313/311,

313/352 [51] Int. Cl ..H0lj 35/10, HOlj 1/05, l-lOlj 1/38 [58] Field ofSearch ..313/55, 311, 330, 352

[56] References Cited UNITED STATES PATENTS Atlee ..313/311 X 1 Oct. 10,1972 2,863,083 12/1958 Schram ..3l3/330 FOREIGN PATENTS OR APPLICATIONS1,464,251 7/ 1969 Germany ..313/55 Primary Examiner-David SchonbergAssistant Examiner-Paul A. Sacher Attorney-Morgan, Finnegan, Durham &Pine [57] ABSTRACT This invention relates to a rotating X-ray targetmade up of three metallic components, i.e., a molybdenum body, a focaltrack of an alloy of tungsten with one or more metal additives and acomponent present in the surface not exposed to electrons comprisingtungsten alone or a tungsten alloy having a lesser amount of theadditive metals.

11 Claims, 3 Drawing Figures P'A'IENTEDHBI 10 I912 13. 697; 7 98 2 I Q@EI 1 (PRIOR ART) FIG. I

I I 2 Q /3 @w 1 1 FIG. 2

FIG. 3

INVENTORS RUDOLF MACHENSCHALK ATTO R NEYS ROTATING X-RAY TARGET X-rayequipment is in wide use for a variety of purposes. Various means areemployed to bombard electrons onto a positively charged surface which isconveniently referred to either as an anode or as an X-ray target. Thereare various types of targets available on the market. These includestationary targets and rotating targets. In general, the X-rays areproduced when the electrons hit the surface of the anode or target underappropriate X-ray generating conditions.

The portion of the surface of the target that is bombarded by electronscan be referred to as the focal track.

The material of which the target surface area or focal track is producedis quite important. The material must be of the proper type to bothwithstand the temperatures of operation and to be an X-ray emitter ofsufficient intensity. In addition, the material must have sufficientductility to withstand conditions of repeated operation. One of theproblems frequently encountered with X-ray targets is the roughening ofthe surface thereby diminishing the efficiency of X-ray emission andrendering emission erratic.

Tungsten is a material commonly used in X-ray targets either alone or asan alloy with small amounts of one or more metal alloying additives.Rhenium is a preferred alloying additive but other alloying additivesinclude osmium, iridium, platinum, technetium, ruthenium, rhodium andpalladium.

The alloying additions to the tungsten serve to a large extent toprevent surface roughening during prolonged operation and also tend toreduce the tendency to form cracks on the surface of the focal track.

Since the alloying elements are relatively expensive and some of themare in short supply, attempts have been made to use the tungsten alloysonly on the surface of the target and to use other materials, such asmolybdenum or molybdenum alloys, i.e., materials with lower specificgravity, as the material for the body of the target. Attempts have alsobeen made to limit the tungsten alloy to just the focal track with theremainder of the surface of the target containing the same material asthe body, e.g., molybdenum. Such X-ray targets create considerabledifficulty because the different surface zones are subject to differentshrinkages, both during formation by powder metallurgical methods andbecause of heat build-up on the focal track and surrounding areas duringelectron bombardment of the target. The consequence is the formation ofcracks at the transitions between the zones, i.e., between the tungstenalloy and the molybdenum.

In the present invention, use is made of a transition layer between thefocal track and the body member which can be of molybdenum or molybdenumalloy. In essence, the X-ray target of this invention comprises a bodyand a surface layer, the body being comprised of molybdenum or an alloyof molybdenum. The portion of the surface comprising the focal track,the area in which the electrons are intended to impinge, is made of analloy of tungsten containing a total of from about 0.05 to 25 percent byweight of one or more of metal alloying additives selected from thegroup consisting of rhenium, osmium, iridium, platinum, technetium,palladium, ruthenium and rhodium. The remainder of the surface, i.e.,the portion of the surface not intended for electron impingement, willalso be made of a tungsten alloy but it will be a tungsten alloy havinga smaller quantity of metal alloying additives than will the tungstenalloy of the focal track. Thus, depending on the alloying additivecontent of the focal track, this additional surface will contain a totalof from about 0.01 to about 4 percent by weight of one or more of theforegoing alloying additives. Alternatively, the surface other than thefocal track can be composed of tungsten alone.

The invention is more fully described in connection with the annexeddrawings in which:

FIG. 1 shows a section of a prior art type rotating X- ray target;

FIG. 2 is a section of the rotating target of this invention; and

FIG. 3 is a section of a rotating target of an alternate embodiment ofthis invention.

In the prior art target of FIG. 1, the body 1 is made of molybdenum andthe circular focal track, where the electrons impinge on the target, isformed of a tungsten alloy containing 10 percent rhenium. Particularlywhen this type of target is made by powder metallurgical methods, crackstend to form at the transition of zones 1 and 2. It will be noted thatthe surface areas other than the focal track 2 are made of molybdenum.

In FIG. 2, focal track 2 is made of a tungsten-rhenium alloy containing10 percent rhenium, and body 1 is made of molybdenum. However, there isan additional layer 3 on the surface of the target not exposed toelectron impingement. That surface 3 is made of tungsten or atungsten-rhenium alloy containing 2 percent rheni- FIG. 3 differs fromFIG. 2 in that the alloy zone ex: tends slightly beyond the electronimpact area in order to shift the transition between zones 2 and 3 tothe flat area of the target, a convenience which aids in manufacture.

The thickness of the layer comprising the focal track can generally bebetween about 0.1 mm and 2 mm. The remainder of the surface can alsohave a thickness within this range. The thickness of the body is notcritical and will depend upon the requirements of the equipment in whichthe target is to be installed. A body of from about 4 to 20 mm inthickness is satisfactory.

The body can be made of molybdenum or a suitable alloy of molybdenumsuch as those used conventionally as bodies for X-ray targets. Suitablealloys include molybdenum alloys containing from about 2 to 10 percentby weight of tungsten or tantalum, molybdenum alloys containing fromabout 0.05 to 1.5 percent by weight of titanium, and molybdenum alloyscontaining from about 0.05 to 0.5 percent by weight of zirconium.

Bodies other than molybdenum may also be employed in the X-ray targetsof this invention. For example, graphite may be employed.

The alloy comprising the focal track in the preferred embodiment of thisinvention should be tungsten alloyed with at least about 1 percent byweight up to about 25 percent by weight of rhenium and, optionally,small amounts, i.e., 0.1 to 5 percent by weight, of osmium, and 0.05 to2 percent by weight, of iridium. Additionally, the presence of fromabout 0.05 to 5 percent by weight of platinum also is useful. In thepreferred embodiment, the total metal alloying additive content will notexceed about 25 percent by weight of the alloy composition. Mostpreferably, the rhenium content will be at least about 5 percent byweight of the alloy composition while the amount of any additionaladditives in total will not exceed the weight of rhenium present.

The remaining part of the surface layer in the preferred embodiment willbe composed of tungsten metal alone or of tungsten with a lesser amountof one or more of the alloying additives, preferably from about 0.01 to4 percent by weight of one of the metal alloying additives. Rhenium isthe preferred alloying additive for the surface layer not exposed toelectron impact.

A convenient target for use in an X-ray tube can be made, for example,by preparing a die and filling it to a predetermined level withmolybdenum powder of particle size range 2 to microns, i.e., where amolybdenum body is desired for the target. By means of a suitabletemplate, the alloy powder for the focal track 2 in particle size 2 to 6microns is then added. Finally, the remaining space is filled with thepowder composition desired to form the zone 3, again in the particlesize of from 2 to 10 microns. Thereupon a pressure of about 4 tons persquare centimeter is employed to compact the powder in the die. Thegreen compacts thus formed are then sintered under a high degree ofvacuum or in an inert or reducing atmosphere such as hydrogen, helium orargon, at a temperature of at least 2,000 C. for 2 hours, and thereuponcooled under the protective atmosphere. The anode is then given itsfinal shape by forging and grinding.

it is found that the products of this invention made in this manner donot suffer from the tendency to crack.

What is claimed is:

l. A rotating X-ray target comprising a body and a surface layer, thebody being comprised of a substance selected from the group consistingof graphite, molybdenum and alloys of molybdenum, the portion of thesurface comprising a focal track being comprised of an alloy of tungstenand a metal alloying additive selected from the group consisting ofrhenium, osmium, iridium, platinum, palladium, technetium, rhodium andruthenium, and the surface of the target not containing the focal trackbeing comprised of a metal selected from the group consisting oftungsten and tungsten alloys having a smaller amount of metal alloyingadditive than in the alloy of the focal track surface.

2. A rotating X-ray target as in claim 1 in which the body is comprisedof molybdenum.

3. A rotating X-ray target as in claim 1 in which the body is comprisedof an alloy of molybdenum.

4. A rotating X-ray target as in claim 1 in which the body is comprisedof graphite.

5. A rotating X-ray target as in claim 1 wherein the focal trackcomprises an alloy of tungsten with about from 1 to 25 percent by weightof rhenium with the remainder of said surface being comprised of a metalselected from the group consisting of tungsten and tungsten alloys witha lesser amount, up to 4 percent by weight, of rhenium.

6. A rotating X-ray target as in claim 1 in which the focal trackcomprises tungsten, from 1 to 25 percent by weight of rhenium and up toa total of 5 percent by weight of at least one metal selected from thegroup consisting of osmium, iriditun and platinum.

7. A rotating anode as in claim 1 wherein the alloy in the focal trackis an alloy of tungsten with about 10 perent b wei t of rhenium. c 8. Xrotefii ng X-ray target comprising a body and a surface layer, the bodybeing comprised of a substance selected form the group consisting ofmolybdenum and alloys of molybdenum, the portion of the surfacecomprising a focal track being comprised of an alloy of tungsten with atleast one metal alloying additive selected from the group consisting ofrhenium, osmiurn, iridium, platinum, palladium, technetium, rhodium andruthenium, and the remainder of the surface layer being comprised of ametal selected from the group consisting of tungsten and tungsten alloysin which the alloying additive metal is present in smaller amount byweight than in the alloy of the focal track.

9. An X-ray target as in claim 8 in which the metals and alloys arepresent in the form of sintered metallic material.

10. An X-ray target as in claim 8 in which tungsten alloys are presentin both the focal track and the surface layer adjacent thereto.

11. A rotating X-ray target as in claim 8 in which rhenium is alloyedwith tungsten in both the focal track and said remainder of the surfacearea.

2. A rotating X-ray target as in claim 1 in which the body is comprisedof molybdenum.
 3. A rotating X-ray target as in claim 1 in which thebody is comprised of an alloy of molybdenum.
 4. A rotating X-ray targetas in claim 1 in which the body is comprised of graphite.
 5. A rotatingX-ray target as in claim 1 wherein the focal track comprises an alloy oftungsten with about from 1 to 25 percent by weight of rhenium with theremainder of said surface being comprised of a metal selected from thegroup consisting of tungsten and tungsten alloys with a lesser amount,up to 4 percent by weight, of rhenium.
 6. A rotating X-ray target as inclaim 1 in which the focal track comprises tungsten, from 1 to 25percent by weight of rhenium and up to a total of 5 percent by weight ofat least one metal selected from the group consisting of osmium, iridiumand platinum.
 7. A rotating anode as in claim 1 wherein the alloy in thefocal track is an alloy of tungsten with about 10 percent by weight ofrhenium.
 8. A rotating X-ray target comprising a body and a surfacelayer, the body being comprised of a substance selected form the groupconsisting of molybdenum and alloys of molybdenum, the portion of thesurface comprising a focal track being comprised of an alloy of tungstenwith at least one metal alloying additive selected from the groupconsisting of rhenium, osmium, iridium, platinum, palladium, technetium,rhodium and ruthenium, and the remainder of the surface layer beingcomprised of a metal selected from the group consisting of tungsten andtungsten alloys in which the alloying additive metal is present insmaller amount by weight than in the alloy of the focal track.
 9. AnX-ray target as in claim 8 in which the metals anD alloys are present inthe form of sintered metallic material.
 10. An X-ray target as in claim8 in which tungsten alloys are present in both the focal track and thesurface layer adjacent thereto.
 11. A rotating X-ray target as in claim8 in which rhenium is alloyed with tungsten in both the focal track andsaid remainder of the surface area.